Wikipedia
Amagat
An amagat is a practical unit of number density. Although it can be applied to any substance at any conditions, it is defined as the number of ideal gas molecules per unit volume at 1 atm (= 101.325 kPa) and 0 °C (= 273.15 K). It is named after Émile Amagat, who also has Amagat's law named after him. The abbreviated form of amagat is "amg."